Glass compositions



United States Patent 3,311,480 GLASS COMPOSITIONS Gordon F. Brewster, Williamson, N.Y., assignor to Bausch & Lomb Incorporated, Rochester, N.Y., a corporation of New York No Drawing. Filed Mar. 18, 1963, Ser. No. 266,024 8 Claims. (Cl. 106-54) This invention relates to novel glass compositions of the type used for ophthalmic segment glass and more particularly to neutral or grey colored segment glass compositions which are compatible with neutral or grey colored crown glasses of the type used for spectacle lenses.

An increased demand for neutral colored spectacle lenses for sun glasses has caused a corresponding increase in the demand for neutral colored multifocal prescription spectacle lenses. Accordingly endeavors have been made to develop a so-called neutral or grey colored segment glass for use with a similarly colored crown glass. Segment glasses of this type should have indices of refraction n in the range of approximately 1.616 to 1.665. The presently preferred compositions disclosed herein have indices of refraction of approximately 1.616 and 1.664. In each of the preferred compositions the index may vary by approximately plus or minus 0.002. These compositions are compatible with and tailored for use with crown glasses having transmittance of 19% and 31%. Accordingly there are four preferred compositions, two having an index of refraction of approximately 1.616 and transmittances of approximately 19% and 31% and those having similar transmittance but an index of refraction of 1.664.

The viscosity of these segment glasses must be compatible with the viscosity of the crown glass forming the spectacle lens. The viscosity is selected, so that, when the segment glass is placed in a countersink in the crown glass, and during fusion therebetween, the crown remains relatively rigid and the segment flows without causing distortion or changes in the curvature of the countersink curve.

It is also important in compounding segment glasses to obtain a high 7 value i.e. where The 7 value is often called constringent and is the ratio of the refractive index, for the D line (Sodium light) minus one to the difference between the refractive indices for the F and C lines (the mean dispersion). A high 'y value is desirable to obtain a relatively low dispersion which tends to overcome chromatic aberrations. It should be understood that in the present case, i.e. with colored segment glasses, the '1 value is of secondary consideration.

The expansion rates of a segment glass must be compatible with a crown glass. Other requirements for segment glasses relate to durability, hardness, said resistance, clear color or transparency, freedom from any cloudy or milky appearance, and color stability.

The segment glasses according to the present invention are not only compatible with the neutral colored crown glasses having similar expansions but also fulfill the necesary physical and optical requirements relating to durability, hardness, acid resistance, clear color or transparency, freedom from any clouding or milky appearance, and color stability.

Briefly, the segment glasses according to the present invention have indices of refraction in the range of approximately 1.616 to approximately 1.665 and a '7 value of approximately 50 to 40 respectively. The segment glass composition consists essentially of the following ingredients given in ranges in weight percent batch basis:

The batch basis relates to the raw batch ingredients which may be compounded according to various techniques, one of which is shown by way of example subsequently in the specification.

The novel glass compositions disclosed herein have a relatively low silica content i.e. in the range of approximately 31 to 34% silica, and incorporate a cobalt-nickel coloring system. The cobalt-nickel coloring system produces a neutral grey color even though the glasses do not contain a significant amount of iron oxide. Previously glasses incorporating an iron-cobalt-nickel coloring system have been disclosed see for example, the patent of James Earl Duncan 2,669,808. Normally these glasses are crown glasses and contain over 50% by weight silica. Such glasses require iron oxide in order to obtain a neutral color.

The oxides may be included in the glasses by adding to the batch the oxides themselves or any desired material that will decompose or react in the melt to produce the specified oxides. For example, the corresponding carbonates, or hydrates may be used. In producing glass compositions according to the present invention the following ingredients have been used to obtain the desired composition.

Oxidg: Batch ingredient i0 Si0 BaO Isa-CO3 ZnO ZnO 1121280 Na CO i 2 TiO ZIOZ ZIOL) Or CaO CaCO MgO MgCO SrO SrCO PbO PbO B 0 B(OH) or borax NiO NiCO The conditions and controls for carrying out the melting, annealing and cooling stepsare subject to wide variation. For example, in some cases a batch of raw ingredients are melted in a refractory pot, crucible or a platinum lined vessel, and in other cases a continuous melting process may be used. Similarly, temperatures, times and conditions vary according to the amount of glass being formed. Therefore, the temperatures and melting conditions recited hereinafter are given by way of illustration and are not intended to limit the scope of the appended claims.

The segment glasses according to the present invention have in some cases been prepared in approximately 10 pound batches in a platinum lined vessel approximately five inches high and five inches in diameter. While platinum is not absolutely necessary it is preferred because of the corrosive action on refractory containers during the melting and fining operations caused by glasses of the present type.

The vessel is preheated to approximately 1300 C. Thereafter, a portion of the mix batch is added to the during fusion. The B also tends to improve the '7 value.

Sodium, and potassium oxides impart a higher expansion to glass than most other oxides. In the present vessel and as the batch melts, additional portions of the 5 glasses they are compounded in order to control the exbatch are added until the charge is completed. Adding pansion characteristics of the segment glasses. The ext-he batch in the aforementioned manner takes approxipansion of the novel segment glasses disclosed herein are mately two hours. The temperature is thus increased to compatible with the respective crown glasses with which approximately 1350 C. and a platinum stirrer which they are used. The alkalis are mixed in order to further may be water cooled is then introduced and used to stir complicate the c-omposition. the melt. During stirring, the melt is maintained at ap- It should be understood, however, that changes in each proximately 1350 C. Stirring at this temperature was of the ingredients have some effect on all of the properties. continued for 8 or more hours. In the present compositions the glasses have been tailored The glass is cooled to approximately 1200" C., the to fit the particular properties desired for crown glasses stirred removed and .the glass cast on a plate which is having compatible characteristics. approximately 200 C. Cooling from 1350 C. to 1200 The following examples set forth several operative em- C., removing the stirrer and casting was accomplished in bodiments and are not to be construed as limiting the approximately one hour. After the casting, the glass is scope of the invention. Examples A, B, C and D repreplaced in an annealing furnace maintained at approxisent the presently preferred embodiments of the invention. mately 550 C., and annealed for approximately two to The optical characteristics of these examples are as folfour hours. Subsequently, the glass is cooled slowly. lows: Example A has an index of refraction of 1.616 and For a piece of glass approximately /2 inch thickness the approximately 19 /2% transmittance; Example B has an glass is cooled at approximately 50 C. per hour to room index of refraction of 1.664 and approximately 19V2% temperature. transmittance; Example C has an index of refraction of Segment glasses according to the present invention may 1.616 and approximately 31% transmittance; and Exbe tailored for particular applications. Such matters ample D has an index of refraction of 1.664 and approxias are contained in the text Properties of Glass by G. mately 31%. The examples are given in weight percent W. Morey are considered in compounding and preparbatch basis.

A B O D For For For For Example A Example B Example 0 Example D ing the novel segment glasses disclosed herein. General- What is claimed is: ly the Morey reference speaks of optical glasses; how- 1. A segment glass composition consisting essentially ever, much of the material may be construed as being 45 of the following ingredients, percent by weight batch more or less directly applicable to segment glasses. Further considerations which are readily apparent to those skilled in the art and which are not clearly set forth herein in detail are contained in the text Modern Ophthalmic Lenses and Optical Glass by Theo. E. Obrig (1935). 5

Additional details about manufacturing optical glass are set forth in The Manufacture of Optical Glass and of Optical Systems, Ordnance Department Document No. 2037, Government Printing Office, 1924. Chapter 3 of the aforementioned Document sets forth the par- 5 ticular processes involved in manufacturing optical glass. Such details are considered to be conventional techniques.

The index of refraction may be regulated by increasing the barium oxide. Strontium oxide, calcium oxide, magnesium oxide, and zinc oxide are also used to regulate the index of refraction, however, these materials have a lesser effect on the index of refraction than the barium oxide. Increasing the lead oxide also increases the index of refraction. It has been found that small quantities of lead oxide are tolerable without adversely affecting the 7 value.

Titanium dioxide and zirconium dioxide also tend to impart a high index of refraction. The titanium and zirconium dioxides, however, are added primarily for improving the acid resistance of the segment glasses.

The viscosity of the glass is effected by B 0 Increasing the B 0 tends to decrease the viscosity. An increase in the silica, however, increases the viscosity. The viscosity is selected so that the crown glass is not damaged basis:

2. A segment glass composition consisting essentially of the following ingredients, percent by weight batch basis:

sio 32.35-34.35 K20 1.02-1.08 N5 0 956-1026 CaO 1.45-1.55 BaO 17.60-18.68 Z110 5.50-5.94 7.10, 5.50-7.00 B203 7.17-7.51 Tio 5.77-7.19 PbO 8.54-9.06 c5 0 0539-0573 NiO .196-.208

3. A segment glass composition consisting essentially of the following ingredients, percent by weight batch basis:

SiO 31.17-33.09 K 0 4.02-4.26 Na O 7.54-8.00 CaO 4.46-4.74 MgO 2.19-2.33 BaO 17.41-18.29 ZnO 1.53-1.63 ZrO 3.39-3.59 B 0 15.83-16.81 SrO L 4.69-4.97 TiO 4.59-4.87 C0 0 .0384-.0404 NiO .l51-.161

4. A segment glass composition consisting essentially of the following ingredients, percent by weight batch basis:

S 31.70-33.66 K 0 1.22-1.30 N3 0 9.35-9.93 C210 1.45-1.55 B30 17.97-19.09 ZnO 4.61-4.89 ZIO 6.35-6.75 B 0 9.01-9.57 T10 6.77-7.19 PbO 8.54-9.06 C0304 N10 .137.145

5. A'segment glass composition consisting essentially of the following ingredients, percent by weight batch basis:

SiO 31.97 K 0 3.48 Na O 8.08 CaO 4.65 MgO 2.28 BaO 18.16 ZnO 1.60 ZrO 4.08 B 0 16.27 SI'O 4.89 TiO 4.56 (30 0. .060 NiO .244

6. A segment glass composition consisting essentially of the following ingredients, percent by weight batch basis:

6 S10 33.35 K 0 1.05 Na O 9.96 CaO 1.50 BaO 18.14 Z 5.77 ZrO 6.80 3 0 7.39 51% 3'33 C0 0 0556 NiO .202

7. A segment glass composition consisting essentially of the following ingredients, percent by weight batch basis:

8. A segment glass composition consisting essentially of the following ingredients, percent by weight batch basis:

S10 32.68 K 0 1.26 5 6 iii a.

B30 18.53 ZnO 4.75 ZfO 6.55 B 0 9.29 T10 6.98 PbO 8.80 C0304 N10 .141

References Cited by the Examiner UNITED STATES PATENTS 2,523,264 9/1950 Armistead 10654 2,523,265 9/1950 Armistead 106-54 2,523,266 9/1950 Armistead 106-54 2,682,134 6/1954 Stookey 10654 3,094,423 6/1963 Davis 106-52 HELEN M. MCCARTHY, Primary Examiner. 

1. A SEGMENT GLASS COMPOSITION CONSISTING ESSENTIALLY OF THE FOLLOWING INGREDIENTS, PERCENT BY WEIGHT BATCH BASIS:
 2. A SEGMENT GLASS COMPOSITION CONSISTING ESSENTIALLY OF THE FOLLOWING INGREDIENTS, PERCENT BY WEIGHT BATCH BASIS: 